Quantum cascade lasers provide a tunable mid-infrared (MIR) light source that can be used for spectroscopic measurements and images. Many chemical components of interest have molecular vibrations that are excited in the MIR region of the optical spectrum, which spans wavelengths between 5 to 25 microns. Hence, measuring the absorption of MIR light at various locations on a sample can provide useful information about the chemistry of the sample as a function of position on the sample.
One class of imaging spectrometers measures the light directly reflected from the sample as a function of position on the sample and wavelength of the illuminating MIR light. The amount of light that is reflected depends on both the chemical and physical attributes of the sample. Hence, comparing spectra generated with direct reflection to absorption with known chemical absorption spectra that are available in libraries presents significant challengers.